EPR studies of the dynamics and phase behaviour of dithiadiazolyl radicals derived from mesogenic precursors.
A series of liquid-crystalline materials based on 4-substituted cyanobiphenyls, RC(6)H(4)C(6)H(4)CN (R = C(5)H(11), C(6)H(13), C(7)H(15), C(8)H(17) and C(12)H(25), commonly referred to as 5CB, 6CB, 7CB, 8CB and 12CB, respectively) were functionalised to give the corresponding dithiadiazolyl organic radicals RC(6)H(4)C(6)H(4)CNSSN(*) (compounds 1(*), 2(*), 3(*), 4(*) and 5(*), respectively). EPR spectra of n-C(12)H(25)C(6)H(4)C(6)H(4)CNSSN(*) (5(*)) reveal that it adopts a dimeric diamagnetic structure in the solid state with a small number of paramagnetic defect sites. Variable temperature electron paramagnetic resonance (EPR) studies reveal a thermally activated rotation about the molecular long axis at temperatures above 314 K. The energy barrier to rotation about the phenylene-dithiadiazolyl bond was estimated as 25 kJ mol(-1) using density functional theory (DFT). At elevated temperatures thermal annealing was also observed, quenching the sample's paramagnetism.
Rawson
Jeremy M
JM
Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK.
Clarke
Caroline S
CS
Bruce
Duncan W
DW